Laser addressable thermal transfer imaging element with an interlayer

ABSTRACT

A thermal transfer donor element is provided which comprises a support, a light-to-heat conversion layer, an interlayer, and a thermal transfer layer. When the above donor element is brought into contact with a receptor and imagewise irradiated, an image is obtained which is free from contamination by the light-to-heat conversion layer. The construction and process of this invention is useful in making colored images including applications such as color proofs and color filter elements.

This is a continuation of application Ser. No. 09/031,941, filed Feb.27, 1998, now U.S. Pat. No. 5,981,136 which is a division of Ser. No.08/632,225, filed on Apr. 15, 1996, issued as U.S. Pat. No. 5,725,989 onMar. 10. 1998.

FIELD OF INVENTION

This invention relates to thermal transfer imaging elements, inparticular, to laser addressable thermal transfer elements having aninterlayer between a radiation-absorbing/thermal conversion layer and atransferable layer. In addition, the invention relates to a method ofusing the thermal transfer element in a thermal transfer system such asa laser addressable system.

With the increase in electronic imaging information capacity and use, aneed for imaging systems capable of being addressed by a variety ofelectronic sources is also increasing. Examples of such imaging systemsinclude thermal transfer, ablation (or transparentization) andablation-transfer imaging. These imaging systems have been shown to beuseful in a wide variety of applications, such as, color proofing, colorfilter arrays for liquid crystal display devices, printing plates, andreproduction masks.

The traditional method of recording electronic information with athermal transfer imaging medium utilizes a thermal printhead as theenergy source. The information is transmitted as electrical energy tothe printhead causing a localized heating of a thermal transfer donorsheet which then transfers material corresponding to the image data to areceptor sheet. The two primary types of thermal transfer donor sheetsare dye sublimation (or dye diffusion transfer) and thermal masstransfer. Representative examples of these types of imaging systems canbe found in U.S. Pat. Nos. 4,839,224 and 4,822,643. The use of thermalprintheads as an energy source suffers several disadvantages, such as,size limitations of the printhead, slow image recording speeds(milliseconds), limited resolution, limited addressability, andartifacts on the image from detrimental contact of the media with theprinthead.

The increasing availability and use of higher output compact lasers,semi-conductor light sources, laser diodes and other radiation sourceswhich emit in the ultraviolet, visible and particularly in thenear-infrared and infrared regions of the electromagnetic spectrum, haveallowed the use of these sources as viable alternatives for the thermalprinthead as an energy source. The use of a radiation source such as alaser or laser diode as the imaging source is one of the primary andpreferred means for transferring electronic information onto an imagerecording media. The use of radiation to expose the media provideshigher resolution and more flexibility in format size of the final imagethan the traditional thermal printhead imaging systems. In addition,radiation sources such as lasers and laser diodes provide the advantageof eliminating the detrimental effects from contact of the media withthe heat source. As a consequence, a need exists for media that have theability to be efficiently exposed by these sources and have the abilityto form images having high resolution and improved edge sharpness.

It is well known in the art to incorporate light-absorbing layers inthermal transfer constructions to act as light-to-heat converters, thusallowing non-contact imaging using radiation sources such as lasers andlaser diodes as energy sources. Representative examples of these typesof elements can be found in U.S. Pat. Nos. 5,308,737; 5,278,023;5,256,506; and 5,156,938. The transfer layer may contain light absorbingmaterials such that the transfer layer itself functions as thelight-to-heat conversion layer. Alternatively, the light-to-heatconversion layer may be a separate layer, for instance, a separate layerbetween the substrate and the transfer layer.

Constructions in which the transfer layer itself functions as thelight-to-heat conversion layer may require the addition of an additiveto increase the absorption of incident radiation and effect transfer toa receptor. In these cases, the presence of the absorber in thetransferred image may have a detrimental effect upon the performance ofthe imaged object (e.g., visible absorption which reduces the opticalpurity of the colors in the transferred image, reduced transferred imagestability, incompatibility between the absorber and other componentspresent in the imaging layer, etc.).

Contamination of the transferred image by the light-to-heat conversionlayer itself is often observed when using donor construcions having aseparate light-to-heat conversion layer. In the cases wherecontamination of the transferred image by such unintended transfer ofthe light-to-heat conversion layer occurs and the light-to-heatconversion layer possesses an optical absorbance that interferes withthe performance of the transferred image (e.g., transfer of a portion ofa black body light-to-heat conversion layer to a color filter array orcolor proof), the incidental transfer of the light-to-heat conversionlayer to the receptor is particularly detrimental to quality of theimaged article. Similarly, mechanical or thermal distortion of thelight-to-heat conversion layer during imaging is common and negativelyimpacts the quality of the transferred coating.

U.S. Pat. No. 5,171,650 discloses methods and materials for thermalimaging using an “ablation-transfer” technique. The donor element usedin the imaging process comprises a support, an intermediate dynamicrelease layer, and an ablative carrier topcoat containing a colorant.Both the dynamic release layer and the color carrier layer may containan infrared-absorbing (light to heat conversion) dye or pigment. Acolored image is produced by placing the donor element in intimatecontact with a receptor and then irradiating the donor with a coherentlight source in an imagewise pattern. The colored carrier layer issimultaneously released and propelled away from the dynamic releaselayer in the light struck areas creating a colored image on thereceptor.

U.S. application Ser. No. 07/855,799 filed March 23, 1992 now U.S. Pat.No. 6,027,849 discloses ablative imaging elements comprising a substratecoated on a portion thereof with an energy sensitive layer comprising aglycidylazide polymer in combination with a radiation absorber.Demonstrated imaging sources included infrared, visible, and ultravioletlasers. Solid state lasers were disclosed as exposure sources, althoughlaser diodes were not specifically mentioned. This application isprimarily concerned with the formation of relief printing plates andlithographic plates by ablation of the energy sensitive layer. Nospecific mention of utility for thermal mass transfer was made.

U.S. Pat. No. 5,308,737 discloses the use of black metal layers onpolymeric substrates with gas-producing polymer layers which generaterelatively high volumes of gas when irradiated. The black metal (e.g.,black aluminum) absorbs the radiation efficiently and converts it toheat for the gas-generating materials. It is observed in the examplesthat in some cases the black metal was eliminated from the substrate,leaving a positive image on the substrate.

U.S. Pat. No. 5,278,023 discloses laser-addressable thermal transfermaterials for producing color proofs, printing plates, films, printedcircuit boards, and other media. The materials contain a substratecoated thereon with a propellant layer wherein the propellant layercontains a material capable of producing nitrogen (N₂) gas at atemperature of preferably less than about 300° C.; a radiation absorber;and a thermal mass transfer material. The thermal mass transfer materialmay be incorporated into the propellant layer or in an additional layercoated onto the propellant layer. The radiation absorber may be employedin one of the above-disclosed layers or in a separate layer in order toachieve localized heating with an electromagnetic energy source, such asa laser. Upon laser induced heating, the transfer material is propelledto the receptor by the rapid expansion of gas. The thermal mass transfermaterial may contain, for example, pigments, toner particles, resins,metal particles, monomers, polymers, dyes, or combinations thereof. Alsodisclosed is a process for forming an image as well as an imaged articlemade thereby.

Laser-induced mass transfer processes have the advantage of very shortheating times (nanoseconds to microseconds); whereas, the conventionalthermal mass transfer methods are relatively slow due to the longerdwell times (milliseconds) required to heat the printhead and transferthe heat to the donor. The transferred images generated underlaser-induced ablation imaging conditions are often fragmented (beingpropelled from the surface as particulates or fragments). The imagesfrom thermal melt stick transfer systems tend to show deformities on thesurface of the transferred material. Therefore, there is a need for athermal transfer system that takes advantage of the speed and efficiencyof laser addressable systems without sacrificing image quality orresolution.

SUMMARY OF THE INVENTION

The present invention relates to a thermal transfer element comprising asubstrate having deposited thereon (a) a light-to-heat conversion layer,(b) an interlayer, and (c) a thermal transfer layer. The thermaltransfer layer may additionally comprise crosslinkable materials.

The present invention also provides a method for generating an image ona receptor using the above described thermal transfer element. An imageis transferred onto a receptor by (a) placing in intimate contact areceptor and the thermal transfer element described above, (b) exposingthe thermal transfer element in an imagewise pattern with a radiationsource, and (c) transferring the thermal transfer layer corresponding tothe imagewise pattern to the receptor, with insignificant or no transferof the light-to-heat conversion layer. When the thermal transfer layercontains crosslinkable materials, an additional curing step may beperformed where the transferred image is subsequently crosslinked byexposure to heat or radiation, or treatment with chemical curatives.

The phrase “in intimate contact” refers to sufficient contact betweentwo surfaces such that the transfer of materials may be accomplishedduring the imaging process to provide a sufficient transfer of materialwithin the thermally addressed areas. In other words, no voids arepresent in the imaged areas which would render the transferred imagenon-functional in its intended application.

Other aspects, advantages, and benefits of the present invention areapparent from the detailed description, the examples, and the claims.

DETAILED DESCRIPTION OF INVENTION

A thermal transfer element is provided comprising a light transparentsubstrate having deposited thereon, in the following order, alight-to-heat conversion (LTHC) layer, a heat stable interlayer, and athermal transfer layer. The substrate is typically a polyester film, forexample, poly(ethylene terephthalate) or poly(ethylene naphthalate).However, any film that has appropriate optical properties and sufficientmechanical stability can be used.

Light-to-heat Conversion Layer.

In order to couple the energy of the exposure source into the imagingconstruction it is especially desirable to incorporate a light-to-heatconversion (LTHC) layer within the construction. The LTHC layercomprises a material which absorbs at least at the wavelength ofirradiation and converts a portion of the incident radiation intosufficient heat to enable transfer the thermal transfer layer from thedonor to the receptor. Typically, LTHC layers will be absorptive in theinfrared region of the electromagnetic spectrum, but in some instancesvisible or ultraviolet absorptions may be selected. It is generallydesirable for the radiation absorber to be highly absorptive of theimaging radiation, enabling an optical density at the wavelength of theimaging radiation in the range of 0.2 to 3.0 using a minimum amount ofradiation absorber to be used.

Dyes suitable for use as radiation absorbers in a LTHC layer may bepresent in particulate form or preferably substantially in moleculardispersion. Especially preferred are dyes absorbing in the IR region ofthe spectrum. Examples of such dyes may be found in Matsuoka, M.,Infrared Absorbing Materials, Plenum Press, New York, 1990, and inMatsuoka, M., Absorption Spectra of Dyes for Diode Lasers, BunshinPublishing Co., Tokyo, 1990. IR absorbers marketed by American Cyanamidor Glendale Protective Technologies, Inc., Lakeland, FL, under thedesignation CYASORB IR-99, IR-126 and IR-165 may also be used. Such dyeswill be chosen for solubility in, and compatibility with, the specificpolymer and coating solvent in question.

Pigmentary materials may also be dispersed in the LTHC layer for use asradiation absorbers. Examples include carbon black and graphite as wellas phthalocyanines, nickel dithiolenes, and other pigments described inU.S. Pat. Nos. 5,166,024 and 5,351,617. Additionally, black azo pigmentsbased on copper or chromium complexes of, for example, pyrazoloneyellow, dianisidine red, and nickel azo yellow are useful. Inorganicpigments are also valuable. Examples include oxides and sulfides ofmetals such as aluminum, bismuth, tin, indium, zinc, titanium, chromium,molybdenum, tungsten, cobalt, iridium, nickel, palladium, platinum,copper, silver, gold, zirconium, iron, lead or tellurium. Metal borides,carbides, nitrides, carbonitrides, bronze-structured oxides, and oxidesstructurally related to the bronze family (e.g. WO_(2.9)) are also ofutility.

When dispersed particulate radiation absorbers are used, it is preferredthat the particle size be less than about 10 micrometers, and especiallypreferred that the particle size be less than about 1 micrometer. Metalsthemselves may be employed, either in the form of particles, asdescribed for instance in U.S. Pat. No. 4,252,671, or as films asdisclosed in U.S. Pat. No. 5,256,506. Suitable metals include aluminum,bismuth, tin, indium, tellurium and zinc.

Suitable binders for use in the LTHC layer include film-formingpolymers, such as for example, phenolic resins (i.e., novolak and resoleresins), polyvinyl butyral resins, polyvinylacetates, polyvinyl acetals,polyvinylidene chlorides, polyacrylates, cellulosic ethers and esters,nitrocelluloses, and polycarbonates. The absorber-to-binder ratio isgenerally from 5:1 to 1:100 by weight depending on what type ofabsorbers and binders are used. Conventional coating aids, such assurfactants and dispersing agents, may be added to facilitate thecoating process. The LTHC layer may be coated onto the substrate using avariety of coating methods known in the art. The LTHC layer is coated toa thickness of 0.001 to 20.0 micrometers, preferably 0.01 to 5.0micrometers. The desired thickness of the LTHC layer will depend uponthe composition of the layer.

A preferred LTHC layer is a pigment/binder layer. A particularlypreferred pigment based LTHC layer is carbon black dispersed in anorganic polymeric binder. Alternatively, other preferred LTHC layersinclude metal or metal/metal oxide layers (e.g. black aluminum which isa partially oxidized aluminum having a black visual appearance).

Interlayer Construction.

The interlayer may comprise an organic and/or inorganic material. Inorder to minimize damage and contamination of the resultant transferredimage, the interlayer should have high thermal resistance.s Preferably,the layer should not visibly distort or chemically decompose attemperatures below 150° C. These properties may be readily provided bypolymeric film (thermoplastic or thermoset layers), metal layers (e.g.,vapor deposited metal layers), inorganic layers (e.g., sol-gel depositedlayers, vapor deposited layers of inorganic oxides [e.g., silica,titania, etc., including metal oxides]), and organic/inorganic compositelayers (thermoplastic or thermoset layers). Organic materials suitableas interlayer materials include both thermoset (crosslinked) andthermoplastic materials. In both cases, the material chosen for theinterlayer should be film forming and should remain substantially intactduring the imaging process. This can be accomplished by the properselection of materials based on their thermal and/or mechanicalproperties. As a guideline, the T_(g) of the thermoplastic materialsshould be greater than 150° C, more preferably greater than 180° C. Theinterlayer may be either transmissive, absorbing, reflective, or somecombination thereof at the imaging radiation wavelength.

The surface characteristics of the interlayer will depend on theapplication for which the imaged article is to be used. Frequently, itwill be desirable to have an interlayer with a “smooth” surface so asnot to impart adverse texture to the surface of the thermallytransferred layer. This is especially important for applicationsrequiring rigid dimensional tolerances such as for color filter elementsfor liquid crystal displays. However, for other applications surface“roughness” or “surface patterns” may be tolerable or even desirable.

The interlayer provides a number of desirable benefits. The interlayeris essentially a barrier against the transfer of material from thelight-to-heat conversion layer. The interlayer can also preventdistortion of the transferred thermal transfer layer material. It mayalso modulate the temperature attained in the thermal transfer layer sothat more thermally unstable materials can be transferred and may alsoresult in improved plastic memory in the transferred material. It isalso to be noted that the interlayer of the present invention, whenplaced over the LTHC layer, is incompatible with propulsively ablativesystems like those of U.S. Pat. Nos. 5,156,938; 5,171,650; and 5,256,506because the interlayer would act as a barrier to prevent propulsiveforces from the LTHC layer from acting on the thermal transfer layer.The gas-generating layers disclosed in those patents also would notqualify as interlayers according to the present invention, as thoselayers must be thermally unstable at the imaging temperatures todecompose and generate the gas to propel material from the surface.

Suitable thermoset resins include materials which may be crosslinked bythermal, radiation, or chemical treatment including, but not limited to,crosslinked poly(meth)acrylates, polyesters, epoxies, polyurethanes,etc. For ease of application, the thermoset materials are usually coatedonto the light-to-heat conversion layer as thermoplastic precursors andsubsequently crosslinked to form the desired crosslinked interlayer.

In the case of thermoplastic materials, any material which meets theabove-mentioned functional criteria may be employed as an interlayermaterial. Accordingly, the preferred materials will possess chemicalstability and mechanical integrity under the imaging conditions. Classesof preferred thermoplastic materials include polysulfones, polyesters,polyimides, etc. These thermoplastic organic materials may be applied tothe light-to-heat conversion layer via conventional coating techniques(solvent coating, etc.).

In the cases of interlayers comprised of organic materials, theinterlayers may also contain appropriate additives includingphotoinitiators, surfactants, pigments, plasticizers, coating aids, etc.The optimum thickness of an organic interlayer is material dependentand, in general, will be the minimum thickness at which transfer of thelight-to-heat conversion layer and distortion of the transferred layerare reduced to levels acceptable for the intended application (whichwill generally be between 0.05 μm and 10 μm).

Inorganic materials suitable as interlayer materials include metals,metal oxides, metal sulfides, inorganic carbon coatings, etc., includingthose which are highly transmissive or reflective at the imaging laserwavelength. These materials may be applied to thelight-to-heat-conversion layer via conventional techniques (e.g., vacuumsputtering, vacuum evaporation, plasma jet, etc.). The optimum thicknessof an inorganic interlayer will again be material dependent. The optimumthickness will be, in general, the minimum thickness at which transferof the light-to-heat conversion layer and distortion of the transferredlayer are reduced to an acceptable level (which will generally bebetween 0.01 μm and 10 μm).

In the case of reflective interlayers, the interlayer comprises a highlyreflective material, such as aluminum or coatings of TiO₂ based inks.The reflective material should be capable of forming an image-releasingsurface for the overlying colorant layer and should remain intact duringthe colorant coating process. The interlayer should not melt or transferunder imaging conditions. In the case where imaging is performed viairradiation from the donor side, a reflective interlayer will attenuatethe level of imaging radiation transmitted through the interlayer andthereby reduce any damage to the resultant image that might result frominteraction of the transmitted radiation with the transfer layer and/orreceptor. This is particularly beneficial in reducing thermal damage tothe transferred image which might occur when the receptor is highlyabsorptive of the imaging radiation. Optionally, the thermal transferdonor element may comprise several interlayers, for example, both areflective and transmissive interlayer, the sequencing of which would bedependent upon the imaging and end-use application requirements.

Suitable highly reflective metallic films include aluminum, chrome, andsilver. Suitable pigment based inks include standard white pigments suchas titanium dioxide, calcium carbonate, and barium sulfate used inconjunction with a binder. The binder may be either a thermoplastic orthermoset material. Preferred binders include high T_(g) resins such aspolysulfones, polyarylsulfones, polyarylethersulfones, polyetherimides,polyarylates, polyimides, polyetheretherketones, and polyamideimides(thermoplastics) and polyesters, epoxies, polyacrylates, polyurethanes,phenol-formaldehydes, urea-formaldehydes, and melamine-formaldehydes(thermosets), etc.

Polymerizable or crosslinkable monomers, oligomers, prepolymers andpolymers may be used as binders and crosslinked to form the desiredheat-resistant, reflective interlayer after the coating process. Themonomers, oligomers, prepolymers and polymers that are suitable for thisapplication include known chemicals that can form a heat resistantpolymeric layer. The layer may also contain additives such ascrosslinkers, surfactants, coating aids, and pigments.

The reflective layer thickness can be optimized with respect to imagingperformance, sensitivity, and surface smoothness. Normally the thicknessof the interlayer is 0.005 to 5 microns, preferably between 0.01 to 2.0microns. Optionally, the reflective interlayer may be overcoated with anon-pigmented polymeric interlayer to allow a better release of colorimage.

Thermal Transfer Layer.

The transfer layer is formulated to be appropriate for the correspondingimaging application (e.g., color proofing, printing plate, colorfilters, etc.). The transfer layer may itself be comprised ofthermoplastic and/or thermoset materials. In many product applications(for example, in printing plate and color filter applications) thetransfer layer materials are preferably crosslinked after laser transferin order to improve performance of the imaged article. Additivesincluded in the transfer layer will again be specific to the end-useapplication (e.g., colorants for color proofing and color filterapplications, photoinitiators for photo-crosslinked orphoto-crosslinkable transfer layers, etc.,) and are well known to thoseskilled in the art.

Because the interlayer can modulate the temperature attained in thethermal transfer layer, materials which tend to be more sensitive toheat than typical pigments may be transferred with reduced damage usingthe process of the present invention. For example, medical diagnosticchemistry can be included in a binder and transferred to a medical testcard using the present invention with less likelihood of damage to themedical chemistry and less possibility of corruption of the testresults. A chemical or enzymatic indicator would be less likely to bedamaged using the present invention with an interlayer compared to thesame material transferred from a conventional thermal donor element.

The thermal transfer layer may comprise classes of materials including,but not limited to dyes (e.g., visible dyes, ultraviolet dyes,fluorescent dyes, radiation-polarizing dyes, IR dyes, etc.), opticallyactive materials, pigments (e.g., transparent pigments, coloredpigments, black body absorbers, etc.), magnetic particles, electricallyconducting or insulating particles, liquid crystal materials,hydrophilic or hydrophobic materials, initiators, sensitizers,phosphors, polymeric binders, enzymes, etc.

For many applications such as color proofing and color filter elements,the thermal transfer layer will comprise colorants. Preferably thethermal transfer layer will comprise at least one organic or inorganiccolorant (i.e., pigments or dyes) and a thermoplastic binder. Otheradditives may also be included such as an IR absorber, dispersingagents, surfactants, stabilizers, plasticizers, crosslinking agents andcoating aids. Any pigment may be used, but for applications such ascolor filter elements, preferred pigments are those listed as havinggood color permanency and transparency in the NPIRI Raw Materials DataHandbook, Volume 4 (Pigments) or W. Herbst, Industrial Organic Pigments,VCH, 1993. Either non-aqueous or aqueous pigment dispersions may beused. The pigments are generally introduced into the color formulationin the form of a millbase comprising the pigment dispersed with a binderand suspended into a solvent or mixture of solvents. The pigment typeand color are chosen such that the color coating is matched to a presetcolor target or specification set by the industry. The type ofdispersing resin and the pigment-to-resin ratio will depend upon thepigment type, surface treatment on the pigment, dispersing solvent andmilling process used in generating the millbase. Suitable dispersingresins include vinyl chloride/vinyl acetate copolymers, poly(vinylacetate)/crotonic acid copolymers, polyurethanes, styrene maleicanhydride half ester resins, (meth)acrylate polymers and copolymers,poly(vinyl acetals), poly(vinyl acetals) modified with anhydrides andamines, hydroxy alkyl cellulose resins and styrene acrylic resins. Apreferred color transfer coating composition comprises 30-80% by weightpigment, 15-60% by weight resin, and 0-20% by weight dispersing agentsand additives.

The amount of binder present in the color transfer layer is kept to aminimum to avoid loss of image resolution and/or imaging sensitivity dueto excessive cohesion in the color transfer layer. The pigment-to-binderratio is typically between 10:1 to 1:10 by weight depending on the typeof pigments and binders used. The binder system may also includepolymerizable and/or crosslinkable materials (i.e., monomers, oligomers,prepolymers, and/or polymers) and optionally an initiator system. Usingmonomers or oligomers assists in reducing the binder cohesive force inthe color transfer layer, therefore improving imaging sensitivity and/ortransferred image resolution. Incorporation of a crosslinkablecomposition into the color transfer layer allows one to produce a moredurable and solvent resistant image. A highly crosslinked image isformed by firsi transferring the image to a receptor and then exposingthe transferred image to radiation, heat and/or a chemical curative tocrosslink the polymerizable materials. In the case where radiation isemployed to crosslink the composition, any radiation source can be usedthat is absorbed by the transfered image. Preferably the compositioncomprises a composition which may be crosslinked with an ultravioletradiation source.

The color transfer layer may be coated by any conventional coatingmethod known in the art. It may be desirable to add coating aids such assurfactants and dispersing agents to provide an uniform coating.Preferably, the layer has a thickness from about 0.05 to 10.0micrometers, more preferably from 0.5 to 2.0 micrometers.

Receiver.

The image receiving substrate may be any substrate suitable for theapplication including, but not limited to, various papers, transparentfilms, LCD black matrices, active portions of LCD displays, metals, etc.Suitable receptors are well known to those skilled in the art.Non-limiting examples of receptors which can be used in the presentinvention include anodized aluminum and other metals, transparentplastic films (e.g., PET), glass, and a variety of different types ofpaper (e.g., filled or unfilled, calendered, coated, etc.). Variouslayers (e.g., an adhesive layer) may be coated onto the image receivingsubstrate to facilitate transfer of the transfer layer to the receiver.

Imaging Process.

The process of the present invention may be performed by fairly simplesteps. During imaging, the donor sheet is brought into intimate contactwith a receptor sheet under pressure or vacuum. A radiation source isthen used to heat the LTHC layer in an imagewise fashion (e.g.,digitally, analog exposure through a mask, etc.) or to perform imagewisetransfer of the thermal transfer layer from the donor to the receptor. AThe interlayer reduces the transfer of the LTHC layer to the receptorand/or reduces distortion in the transferred layer. Without thisinterlayer in thermal mass transfer processes addressed by radiationsources, the topography of the transfer surface from the light-to-heatconversion layer may be observably altered. A significant topography ofdeformations and wrinkles may be formed. This topography may beimprinted on the transferred donor material. This imprinting of theimage alters the reflectivity of the transferred image (rendering itless reflective than intended) and can cause other undesirable visualeffects. It is preferred that under imaging conditions, the adhesion ofthe interlayer to the LTHC layer be greater than the adhesion of theinterlayer to the thermal transfer layer. In the case where imaging isperformed via irradiation from the donor side, a reflective interlayerwill attenuate the level of imaging radiation transmitted through theinterlayer and thereby reduce any transferred image damage that mayresult from interaction of the transmitted radiation with the transferlayer and/or the receptor. This is particularly beneficial in reducingthermal damage which may occur to the transferred image when thereceptor is highly absorptive of the imaging radiation.

A variety of light-emitting sources can be utilized in the presentinvention. Infrared, visible, and ultraviolet lasers are particularlyuseful when using digital imaging techniques. When analog techniques areused (e.g., exposure through a mask) high powered light sources (e.g,xenon flash lamps, etc.) are also useful. Preferred lasers for use inthis invention include high power (>100 mW) single mode laser diodes,fiber-coupled laser diodes, and diode-pumped solid state lasers (e.g.,Nd:YAG and Nd:YLF). Laser exposure dwell times should be from about 0.1to 5 microseconds and laser fluences should be from about 0.01 to about1 Joules/cm².

During laser exposure, it may be desirable to minimize formation ofinterference patterns due to multiple reflections from the imagedmaterial. This can be accomplished by various methods. The most commonmethod is to effectively roughen the surface of the donor material onthe scale of the incident radiation as described in U.S. Pat. No.5,089,372. This has the effect of disrupting the spatial coherence ofthe incident radiation, thus minimizing self interference. An alternatemethod is to employ the use of an antireflection coating on the secondinterface that the incident illumination encounters. The use ofanti-reflection coatings is well known in the art, and may consist ofquarter-wave thicknesses of a coating such as magnesium fluoride, asdescribed in U.S. Pat No. 5,171,650. Due to cost and manufacturingconstraints, the surface roughening approach is preferred in manyapplications.

The following non-limiting examples fuirther illustrate the presentinvention.

EXAMPLES

Materials used in the following examples are available from standardcommercial sources such as Aldrich Chemical Co. (Milwaukee, WI) unlessotherwise specified. The preparation of hydantoin hexacrylate used inExample 2 is described for Compound A in U.S. Pat. Nos. 4,249,011 and4,262,072.

Laser Imaging Procedure A

The colorant coating side of a thermal transfer donor was held inintimate contact with a 75 mm×50 mm×1 mm glass slide (receptor) in avacuum chuck such that the laser was incident upon the substrate (PET)side of the donor and normal to the donor/receptor surface. The vacuumchuck was attached to an X-Y translation stage such that it could bescanned in the plane of the donor/receptor surface, allowing laserexposure over the entire surface. A CW(continuous wave) Nd:YAG lasersystem was used for exposure, providing up, to 14.5 Watts at 1064 nm inthe film plane. The laser had a Gaussian spatial profile with the spotsize tailored using external optics. An acoustic-optic modulator allowedcontrol of the laser power from −0 to 80%, the laser pulse width from−20 ns to CW. The X-Y stage and laser power, pulse width and repetitionrate were computer controlled allowing programmed patterns to be imaged.

Laser Imaging Procedure B

The colorant coating side of a thermal transfer donor was held inintimate contact with a 75 mm×50 mm×1 mm glass slide (receptor) in avacuum chuck such that the laser was incident upon the substrate (PET)side of the donor. The vacuum chuck was attached to a one dimensionaltranslation stage such that it could be scanned in the plane of thedonor/receptor surface, allowing laser exposure over the entire surface.An optical system comprised of a CW Nd:YAG laser, acousto-opticmodulator, collimating and beam expanding optics, an optical isolator, alinear galvonometer and an f-theta scan lens was utilized. The Nd:YAGlaser was operating in the TEM 00 mode, and produced a total power of7.5 Watts on the image plane. Scanning was accomplished with the highprecision linear Cambridge Technology Galvonometer. The laser wasfocused to a Gaussian spot with a measured diameter of 140 microns atthe I/e² intensity level. The spot was 20 held constant across the scanwidth by utilizing an f-theta scan lens. The laser spot was scannedacross the image surface at a velocity of 7.92 meters/second. Thef-theta scan lens held the scan velocity uniform to within 0.1%, and thespot size constant to within ±3 microns.

Example 1 (Comparative Example)

This example demonstrates the preparation and use of a thermal transferdonor without an interlayer.

A black aluminum (partially oxidized Al, AlO_(x)) light-to-heatconversion layer with a transmission optical density (TOD=−logT, where Tis the measured fractional transmission) of 0.53 at 1060 nm was coatedonto a 4 mil poly(ethylene terephthalate) (PET) substrate via reactivesputtering of Al in an Ar/O₂ atmosphere in a continuous vacuum coateraccording to the teachings of U. S. Pat. No. 4,430,366. This AlO_(x)light-to-heat conversion layer was then overcoated with a red color inkwith 26.5 weight % total nonvolatiles content (CRY-S089, produced byFuji-Hunt Electronics Technology Co., LTD, Tokyo, Japan) using a #5coating rod and dried to produce a thermal transfer donor.

This donor was then tested for transfer of the thermal transfer layer toa glass slide receptor, which had been precoated with a vinyl acryliccopolymer (Wallpol 40148-00, Reichhold Chemicals, Inc. Research TrianglePark, N.C.). The above-described Laser Imaging Procedure A was employed,the laser spot size diameter (1/e²) was 100 μm, the power at the filmplane was 8.4 watts, and exposures were performed at pulse widths of 4,6, 8 and 10 microseconds.

The results showed that, although color images were formed on thereceptor at the four different pulse widths, the images were discolored.A microscopic examination of the images revealed that the red colorimages were contaminated with the black aluminum light-to-heatconversion layer which had transferred from the donor.

Example 2

This example demonstrates the preparation and use of a thermal transferdonor with a thermoset interlayer.

The same black aluminum light-to-heat conversion layer referenced inExample I was coated with a 5 weight % solution of hydantoin hexacrylate(49 parts by weight), 1,6-hexanediol diacrylate (49 parts by weight) and2,2-dimethoxy-2-phenylacetophenone (2 parts by weight) in 2-butanoneusing a #5 coating rod, dried and then radiation crosslinked viaexposure in a Radiation Polymer Corporation (Plainfield, Ill.) UVProcessor Model No. QC1202AN3TR (medium pressure uv lamp, total exposureca. 100 millijoules/cm², N₂ atmosphere) to produce an interlayer. Thecured interlayer was smooth, non-tacky, and resistant to many organicsolvents including 2-butanone. The cured interlayer was then overcoatedwith the same red color ink employing the same coating procedures asdescribed in Example 1.

The resulting donor was tested for transfer of the thermal transferlayer to a glass slide receptor employing laser imaging conditionsidentical to those described in Example 1.

A microscopic examination of the images on the receptor clearlyindicated that the red color images were free of black aluminumcontamination. The same microscopic examination of the imaged area ofthe donor showed that the interlayer and black aluminum light-to-heatconversion layer remained intact ofi the thermal transfer donor.

Example 3

This example demonstrates the preparation and use of a thermal transferdonor with a thermoplastic interlayer.

The same black aluminum light-to-heat conversion layer referenced inExample 1 was coated with a 10 weight % solution of Radel A-100polysulfone resin (Amoco Performance Products, Inc., Alpharetta, GA) in1, I,2-trichloroethane using a # 12 coating rod. The Radel A-100interlayer was then overcoated with the same red color ink and employingthe same coating procedures as described in Example 1.

The resulting donor was tested for transfer of the thermal transferlayer to a glass slide receptor employing laser imaging conditionsidentical to that described in Example 1. The results again showed thatthe color images were formed on the receptor at the four different pulsewidths. A microscopic examination of the images on the receptor clearlyindicated that the red color images were free of black aluminumcontamination. The same microscopic examination of the imaged area ofthe donor showed again that the interlayer and black aluminumlight-to-heat conversion layer remained intact on the thermal transferdonor.

Example 4

This example demonstrates the preparation and use of a thermal transferdonor with an inorganic interlayer.

A black aluminum (AlO_(x)) coating was deposited onto 4 milpoly(ethylene terephthalate) (PET) substrate via evaporation of Al in apartial O₂ atmosphere according to the teachings of U.S. Pat. No.4,430,366. The transmission and reflection spectra of the resultantcoating on PET were measured from both the black aluminum coating sideand the substrate (PET) side using a Shimadzu MPC-3100 spectrophotometerwith an integrating sphere (Shimadzu Scientific Instruments, Inc.,Columbia, Md.). The transmission optical densities (TOD=−logT, where Tis the measured fractional transmission) and reflection opticaldensities (ROD=−logR, where R is the measured fractional reflectance) at1060 nm are listed in Table 1. The thickness of the black aluminumcoating was determined to be 1100 A by profilometry after masking andetching a portion of the coating with 20 percent by weight aqueoussodium hydroxide.

TABLE 1 Side of TOD ROD Incident Beam (at 1060 nm) (at 1060 nm) Coating1.047 0.427 Substrate 1.050 0.456

An alumina interlayer (approximately 1000 Å thick) was coated onto theblack aluminum surface by evaporation of Al₂O₃ in a vacuum coater.

A colorant coating solution was prepared by combining and mixing 2 gramsof 10 weight % Heucotech GW3451 Lot 3F2299 PG 7 binderless pigmentdispersion (Heucotech, Ltd., Fairless Hills, Pa.), 0.917 grams deionized1420, 0.833 grams of 18 weight % Elvacite® 2776 in water (prepared bymixing 0.8 g of a 25% ammonia solution and 22 g water, and 5 g ofElvacite® 2776 from ICI Acrylics, Wilmington, DE) and 10 drops of a 1weight % solution of FC-170C fluorochemical surfactant (3M, St. Paul,Minn.). This green coating solution was coated onto the alumina surfaceusing a #4 coating rod. The resultant green donor media was dried at 50°C for 2 minutes. The same green solution was coated onto the blackaluminum (AlO_(x)) surface of the light-to-heat conversion film that didnot have the alumina interlayer using a #4 coating rod. The resultantgreen donor media was dried at 50° C for 2 minutes.

These two donors, one with an alumina interlayer and the other without,were imaged onto glass receptors to make color filter elements for aliquid crystal display via laser induced thermal transfer imaging (LITI)utilizing the above-described Laser Imaging Procedure A. For theseexperiments, the laser spot diameter size (1/e²) was 100 μm, the powerat the film plane was 4.2 Watts, and the pulse width was 8 μsec. Theamount of black aluminum contamination of the resultant color filterswas then quantified via digitizing micrographs of the correspondingcolor filters and subsequent image analysis with IPLAB Spectrum-NV(Signal Analytics Corp., Vienna, Va.). The analyses indicate that theaverage area of the black aluminum light-to-heat conversion layertransferred to the receptor per imaged spot was 4 μm² black aluminumcontamination per spot for the sample with the alumina interlayer vs.125 μm² for the sample with no interlayer.

These results demonstrate the efficacy of the interlayer in improvingtransferred image quality and preventing image contamination with thelight-to-heat conversion layer.

Example 5

This example demonstrates the preparation and use of a thermal transferdonor with a thermoset interlayer and a crosslinkable transfer layer.

A carbon black light-to-heat conversion layer was prepared by coating anaqueous dispersion of carbon black in a radiation curable resin onto a 2mil PET substrate with a Yasui Seiki Lab Coater, Model CAG-150 (YasuiSeiki Co., Bloomington, Ind.) using a microgravure roll of 90 helicalcells per lineal inch. The coating was subsequently in-line dried anduv-cured on the coater before windup. The coating solution consisted of16.78 weight % of a urethane-acrylate oligomer (Neorad NR-440 fromZeneca Resins, Wilmington, MA), 0.84 weight % of2-hydroxy-2-methyl-1-phenyl-1-propanone photoinitiator (Darocur 1173,Ciba-Geigy, Hawthorne, N.Y.), 2.38 weight % of carbon black (SunsperseBlack 7, Sun Chemical, Amelia, Ohio), and 80 weight % of water having apH of ca. 8.5.

The light-to-heat conversion layer was then overcoated with aninterlayer coating utilizing the above-described coater with amicrogravure roll of 110 helical cells per lineal inch. After theinterlayer was coated, it was in-line dried and uv-cured. The interlayercoating solution consisted of 19.8 weight % of a urethane-acrylateoligomer (Neorad NR-440 from Zeneca Resins, Wilmington, Mass.), 1.0weight % of 2-hydroxy-2 methyl-1-phenyl-1-propanone photoinitiator(Darocur 1173, Ciba-Geigy, Hawthorne, N.Y.), and 79.2 weight % of waterhaving a pH of 8.5.

The colorant transfer layer was a 15 weight % nonvolatiles contentaqueous dispersion prepared by Penn Color, Doylestown, Pa., andconsisted of Pigment Green 7 and Elvacite 2776 (ICI Acrylics, Inc.,Wilmington, Del.) neutralized with dimethylethanolamine at a 3:2pigment/binder ratio, containing 4 weight % Primid XL-552 (EMS AmericanGrilon, Sumter, S.C.) relative to the polymer, and 1 weight % TritonX-100 relative to the total nonvolatiles content. This dispersion wascoated onto the interlayer using a #3 coating rod and the resultantcoating was dried at 80° C for 3 minutes.

The colorant layer was then transferred to two glass slides usingimaging conditions employing Laser Imaging Procedure B to produce LCDcolor filter elements. The colorant transferred to the glass slides(lines ca. 90 micrometers wide with a line-to-line spacing of ca. 150micrometers) with no contamination of the carbon black layer.Microscopic examination of the donor sheet showed the carbon blackcomposite light-to-heat conversion layer and the protective clearinterlayer were intact. One of the color filter elements was then placedin an oven and heated at 200° C in a nitrogen atmosphere for one hour inorder to activate the crosslinking chemistry between the Primid XL552and the Elvacite 2776. The other color filter element was not heated,but maintained at ambient temperature. Each of the resultant colorfilter elements was then cut into three ca. 25 mm×37 mm sections. One ofthe sections derived from each of these color filter elements was thenimmersed in 10 ml of 1-methyl-2-pyrrolidinone for 10 minutes. The colorfilter elements were then removed from the immersion solvents. Thevisible spectra of the solutions resulting from extractions of thesecolor filter elements were then obtained in a quartz cuvette with a 1 cmpath length on a Shimadzu MPC-3100 spectrophotometer. These spectraindicated the λ_(max) of the color cell array extracts to be at ca. 629nm, with good chemical resistance of each of the color cell arrayelements corresponding to low absorbance of its 1-methyl-2-pyrrolidinoneextract at 629 nm. The corresponding results of the chemical resistancetesting of the crosslinked and uncrosslinked color filter element areprovided in Table 2.

TABLE 2 Color Filter Element Absorbance of Corresponding 1-Methyl-2-Designation Pyrrolidinone Extract (629 nm) uncrosslinked color array0.53 crosslinked color array 0.04 neat solvent (1-methyl-2- 0.04pyrrolidinone)

The above results demonstrate the efficacy of the interlayer inimproving the quality of the transferred image and the effectiveness ofcrosslinking the transferred coating to improve its correspondingsolvent resistance.

Example 6 (Comparative Example)

This example demonstrates the preparation and use of a thermal transferdonor without an interlayer.

A carbon black light-to-heat convesion film with an absorbance of 1.35at 1064 nm, was prepared by coating an aqueous dispersion of carbonblack in a radiation curable resin onto a 2 mil PET substrate with aYasui Seiki Lab Coater, Model CAG-150 (Yasui Seiki Co., Bloomington,Ind.) using a microgravure roll of 90 helical cells per lineal inch. Thecoating was subsequently in-line dried and uv-cured on the coater beforewindup. The coating solution consisted of 1 part of carbon black(Sunsperse black, Sun Chemical, Amelia, Ohio), 7 parts of NR-440 (acrosslinkable urethane acrylate oligomer from Zeneca Resins, Wilmington,Mass.), and 0.35 part of a photoinitiator (Darocur 1173 from Ciba-Geigy,Hawthorne, N.Y.) at 35 wt% total solid in water to give a light-to-heatconversion coating with a 4.5 gm dry thickness.

The light-to-heat conversion layer was overcoated with a clearinterlayer, followed by a colorant layer. Using a #5 coating rod, anaqueous solution containing 12.5 wt % NR-440 and 0.6 wt % Darocur 1173was coated, dried at 80° C for 2 minutes and UV crosslinked to provide acolor topcoat with a heat stable, smooth release surface. The colortransfer layer was applied by coating the green color ink of Example 5at 15 wt% total solid using a #5 coating rod and drying for 3 min at 60°C to give a 1 lm thick colorant layer.

The donor thus prepared was tested for imagewise transfer of the thermaltransfer layer to a black chrome coated glass receptor, which had anabsorbance of 2.8 at 1064 nm. The color donor sheet was imaged with aline pattern and transferred onto the glass receptor (75 mm×50 mm×1.1mm). Imaging was performed in a flat-bed imaging system, using a Nd:YAGlaser operating at 7.5 W on the donor film plane with a 140 μm laserspot size (1/e²diameter). The laser scan rate was 4.5 m/s. Image datawere transferred from a mass-memory system and supplied to anacoustic-optic modulator which performed the imagewise modulation of thelaser. During the imaging process, the donor sheet and the receptor wereheld in intimate contact with vacuum assistance.

A microscopic inspection of the resultant image on the receptorindicated that the imaged lines possessed a uniform line width of 89 pm.Damage (e.g., roughened surface, cracks, bubbles, color variation, etc.)was observed to be present at the central portion of each of thetransferred colorant lines.

Example 7

This example demonstrates the preparation and use of a thermal transferdonor with a vapor-coated aluminum reflective interlayer coated over aLTHC layer comprising carbon black dispersed in a crosslinked organicbinder.

The donor used in this example was the same as that used in Example 6,except that a vapor-coated aluminum reflective interlayer was coated onthe light-to-heat conversion layer prior to coating the color transferlayer. The aluminum coating was determined to have 85.8% reflection at1064 nm.

The donor was tested for imagewise transfer of the thermal transferlayer to a black chrome coated glass receptor using the same methoddescribed in Example 6.

A microscopic inspection of the resultant image indicated that the imagelines were of good overall quality with a uniform linewidth of 82 μm. Noobvious sign of thermal damage was observed in the central portion ofthe transferred lines.

Example 8

This example demonstrates the preparation and use of a thermal transferdonor with a white reflective interlayer.

The donor used in this example was the same as that used in Example 6,except that a white reflective interlayer was coated on thelight-to-heat conversion layer prior to the other coatings. The whitereflective layer was prepared by coating a white correction ink at 17.3wt % total solid (Pentel Correction Pen™ ink) with a #3 coating rod,followed by drying at 80° C for 2 min. The coating was determined tohave a reflectivity of 22.5% at 1064 nm.

The donor was tested for imagewise transfer of the thermal transferlayer to a black chrome coated glass receptor using the same methoddescribed in Example 6.

A microscopic inspection of the resultant image indicated that the imagelines were of good overall quality with a uniform linewidth of 82 μm. Noobvious sign of thermal damage was observed in the central portion ofthe transferred lines.

Example 9

The donors used in this example were the same as those used in Examples6-8, except that a carbon black light-to-heat conversion layer with anabsorbance of 0.94 at 1060 nm was used. This light-to-heat conversionlayer was prepared by the same method as described in Example 6, exceptthat the coating solution contained 27 wt % total solids instead of 35wt %.

The donors were tested for imagewise transfer of the thermal transferlayer to a black chrome coated glass receptor using the same methoddescribed in Example 6.

The results of a microscopic inspection of the resultant images on thereceptors are summarized in Table 3.

TABLE 3 Effect of Reflective Interlayer on Image Quality (5.3 m/sec ScanSpeed) Damage to Donor Linewidth (μm) transferrred line Control 90 someAl Interlayer 97 some White Interlayer 100 none

The results indicate that images transferred from the donor with a whiteinterlayer (22.5% R, 46% T) suffered the least damage.

These results demonstrate the efficacy of a reflective interlayer in theimprovement of transferred image quality and the prevention of thermaldamage of the transferred material.

Example 10

This example demonstrates the preparation and use of a thermal transferdonor with a reflective aluminum interlayer coated over a black aluminumLTHC layer.

A black aluminum (partially oxidized Al, AlO_(x)) light-to-heatconversion layer of approximately 800 Å was coated onto a 4 milpoly(ethylene terephthalate) (PET) substrate via reactive sputtering ofAl in an Ar/O₂ atmosphere in a continuous vacuum coater according to theteachings of U. S. Pat. No. 4,430,366. Approximately 100 Å of Al wasthen sputtered onto the AlO_(x) light-to-heat conversion layer in an Aratmosphere with the same continuous vacuum coater. The resultantmaterial containing the reflective aluminum interlayer was thenovercoated with an aqueous green color ink of the composition shown inTable 4 using a #4 coating rod and dried at 60° C to produce a thermaltransfer donor.

TABLE 4 Composition of Aqueous Green Ink Coating Solution CoatingComponent Percent by Weight PG-7 Pigment* 9.1 ICI Elvacite 2776* 5.3Triethyl-O-acetyl-citrate 0.3 Dimethylethanolamine 1.1 3M FC-430Surfactant 0.04 H₂O 84.2 *A dispersion of PG-7 pigment in Elvacite 2776was obtained from Penn Color, Doylestown, PA.

This donor was then tested for thermal transfer to a glass slidereceptor to produce a color filter element for a liquid crystal display.The above-described Laser Imaging Procedure A was employed and the laserspot diameter was 100 μm (1/e²), the power at the film plane was 8.4watts, and exposures were performed at pulse widths of 4, 6 and 8microseconds.

The results showed that the transferred images were essentially freefrom black aluminum contamination under the above-described imagingconditions.

Reasonable variations and modifications are possible from the foregoingdisclosure without departing from either the spirit or scope of thepresent invention as recited in the claims.

What is claimed is:
 1. A thermal transfer element comprising: asubstrate; a light-to-heat conversion layer including a radiationabsorber that converts light energy to thermal energy; and a thermaltransfer layer comprising medical diagnostic chemistry; furthercomprising an interlayer, between the light-to heat conversion layer andthe thermal transfer layer, that does not visibly distort or chemicallydecompose at temperatures below 150° C.
 2. The thermal transfer elementof claim 1, wherein the interlayer comprises a metal, inorganiccompound, crosslinked polymer, thermoplastic polymer with a T_(g) of atleast 150° C., or a mixture thereof.
 3. A thermal transfer elementcomprising: a substrate; a light-to-heat conversion layer including aradiation absorber that converts light energy to thermal energy; and athermal transfer layer comprising an enzyme; further comprising aninterlayer, between the light-to-heat conversion layer and the thermaltransfer layer, that does not visibly distort or chemically decompose attemperatures below 150° C.
 4. A thermal transfer element comprising: asubstrate; a light-to-heat conversion layer disposed over the substrateand including a radiation absorber an interlayer disposed over thelight-to-heat conversion layer and resistant to thermal decompositionbelow at least 150° C; and a thermal transfer disposed over theinterlayer and comprising medical diagnostic chemistry.
 5. The thermaltransfer element of claim 4, wherein the medical diagnostic chemistrycomprises an enzymatic indicator.
 6. The thermal transfer element ofclaim 4, wherein the medical diagnostic chemistry comprises a chemicalindicator.
 7. The thermal transfer element of claim 4, wherein thethermal transfer layer further comprises a binder.
 8. A method fortransferring medical diagnostic chemistry to a receptor, comprising:contacting the receptor with a thermal transfer layer of a thermaltransfer element, the thermal transfer layer comprising the medicaldiagnostic chemistry and the thermal transfer element further comprisinga substrate and a light-to-heat conversion layer having a radiationabsorber for convening light energy into thermal energy; selectivelyexposing the radiation absorber to radiation to generate thermal energyaccording to a pattern; and thermal transferring the medical diagnosticchemistry to the receptor according to the pattern; wherein the thermaltransfer element further comprises an interlayer between thelight-to-heat conversion layer and the thermal transfer layer andresistant to thermal decomposition below at least 150° C.
 9. A methodfor transferring medical diagnostic chemistry to a receptor, comprising:contacting the receptor with a thermal transfer layer of a thermaltransfer element, the thermal transfer layer comprising the medicaldiagnostic chemistry and the thermal transfer element further comprisinga substrate and a light-to-heat conversion layer having a radiationabsorber for converting light energy into thermal energy, and aninterlayer between the light to heat conversion layer and the thermaltransfer layer and resistant to thermal decomposition below at least150° C; selectively exposing the radiation absorber to radiation togenerate thermal energy according to a pattern; and thermallytransferring the medical diagnostic chemistry to the receptor accordingto the pattern without transfer of any substantial portion of theinterlayer.